A stump grinder is a specialized machine featuring a powerful, rotating wheel equipped with carbide teeth designed to chip away at wood. This process converts the remaining tree stump into a pile of wood shavings, or mulch, rather than physically uprooting the entire structure. While a stump grinder’s primary purpose is to eliminate the main stump, it can also be used to address the surrounding root system. Dealing with the roots allows for a cleaner area for replanting or construction, but this task requires careful consideration of the machine’s capabilities and safety precautions. The process is effective, provided the operator understands the limitations and risks involved in cutting below the soil line.
Grinding Depth and Horizontal Limits
The ability of a stump grinder to remove roots is directly tied to its physical reach, both vertically and horizontally. For most landscaping purposes, grinding the main stump to a depth of four to six inches below the soil surface is sufficient to prevent regrowth and allow for new sod or topsoil. Standard commercial and rental grinders are capable of reaching significantly deeper, often between 13 to 20 inches below grade.
The maximum depth pursued should be dictated by the intended use of the area. Horizontally, a tree’s primary roots often radiate outward from the trunk, diminishing in size as they spread. To effectively target these roots after the main stump is gone, extend the grinding area at least one to two times the diameter of the original stump. This lateral extension ensures that major surface roots, which can cause lawn bumps or interfere with future planting, are adequately pulverized.
The power and size of the equipment also determine the practical limits of root removal. Larger, self-propelled grinders have the horsepower to cut through large lateral roots far from the central stump. Smaller, walk-behind units may struggle with thick roots located more than a few feet away, making the effort less efficient.
Identifying and Avoiding Underground Dangers
The unknown presence of subsurface obstructions is a major hazard when using a stump grinder on roots. Before attempting to grind any root below the visible surface, you must contact 811, the national “Call Before You Dig” hotline. This free service ensures that professional locators visit the site to mark the approximate locations of buried public utilities, such as gas lines, power cables, and water mains.
Striking a utility line with the high-speed carbide teeth of a grinder can lead to catastrophic results, including electrocution, fire, or explosion. Even non-utility hazards, which are not marked by the 811 service, pose risks to the operator and the machine. These include buried rocks, concrete debris, rebar, or abandoned irrigation lines.
Hitting a large, unyielding object like a rock or concrete can cause a violent kickback of the machine. Any non-wood material struck by the wheel becomes a high-velocity projectile, capable of damaging property or causing severe injury. Irrigation pipes, typically shallowly buried, are particularly vulnerable and must be manually located and temporarily removed or bypassed before grinding proceeds.
Step-by-Step Techniques for Root Grinding
The process of grinding roots should be performed only after the main stump is removed and all underground dangers are marked. The first preparatory step is to trim any remaining stump material as close to the ground as possible to reduce the grinder’s initial workload. Clear the immediate area of any loose debris, such as small stones or gravel, that could be thrown by the cutting wheel.
Position the grinder so the cutting wheel is centered over the first exposed root section you intend to remove. Engage the wheel and begin the grinding process by moving the cutter head in a slow, controlled side-to-side sweeping motion across the width of the root. This technique shaves off small amounts of wood with each pass, preventing the engine from bogging down.
After completing a full sweep across the root, lower the cutter wheel approximately one-half to one inch deeper into the material before beginning the next pass. By working in these shallow, incremental passes, you maintain consistent control and allow the machine to operate efficiently. Continue this process, following the exposed root system outward from the main stump area, until all visible surface roots are ground down to the desired depth below grade.
Once the grinding is complete, the resulting wood chips should be raked out of the trench to expose any roots that may have been missed. The finer wood chip mixture can then be used as mulch or mixed with new topsoil to fill the remaining hole.